Large-capacity power-generating nuclear fission reactor plants normally have several hundred sealed tubular containers for housing fissionable fuel. To facilitate periodic refueling, which commonly is performed by replacing fractional portions of the total fuel at intervals and rearranging other fractional portions, these fuel rods or pins are conventionally assembled into bundles or groups of elements which can be manipulated as a single composite unit.
The fuel rods of each bundle are held mutually parallel and spaced apart by mechanical means. A typical fuel bundle comprises, for example, an 8.times.8 or 9.times.9 array of spaced fuel rods. Each fuel rod is usually more than 10 ft. long, e.g., 14 ft., and approximately 1/2 inch in diameter.
To inhibit the fuel rods from bowing and vibrating due to high heat and high velocity of the coolant flowing past, the fuel rods are maintained in their spaced-apart relation by a plurality of spacers positioned at intervals along their length. Typical spacers for fuel rods comprise a lattice having a plurality of openings arranged in the designated pattern for spacing the parallel aligned fuel rods. The assembled bundle of a group of spaced-apart, parallel aligned fuel rods additionally each have their ends supported in corresponding sockets of upper and lower tie plates.
The typical fuel bundle assembly also comprises an open-ended tubular channel of suitable cross section, such as square, which surrounds the fuel rods. The fuel channel directs the flow of coolant longitudinally along the surface of the fuel rods and channels the neutron-absorbing fission control rods, which reciprocate longitudinally intermediate a 2.times.2 array of channeled fuel bundle assemblies.
A bail is connected to the upper tie plate. When a hoist is coupled to the bail, the fuel bundle assembly can be lifted and transported as a unit. When supported by a hoist, the fuel bundle assembly hangs in a generally vertical position.
A conventional new fuel storage pool has a rack comprising a plurality of cells for receiving and storing new fuel bundle assemblies. To store a new fuel bundle assembly in a cell of a conventional rack, the new fuel bundle assembly must be hoisted over the open top of the cell and then lowered into the cell. Each cell has a generally square cross section and is vertically disposed so that the fuel bundle stored therein will be held in a generally upright position as it bears against the walls of the cell.
The foregoing conventional means for storing fuel bundle assemblies in a new fuel storage pool has several disadvantages. First, it is undesirable from a safety standpoint to transport fuel along a path overlying stored fuel. In the event that the fuel bundle being transported were to break away from the hoist, the fuel would fall on top of any fuel stored below, thereby increasing the attendant hazards and complicating the clean-up operation. Second, if fuel bundle assemblies having a height h must be transported over stored fuel bundle assemblies of height h, then the new fuel storage pool must have a depth equal to at least 2h to ensure that the fuel bundle assemblies are entirely submerged in water during transport. The greater the depth of the new fuel storage pool, the greater are the attendant construction costs.